Thyroid Medicines Information

 

Thyroid Medicines

In hyperthyroidism there is an excessive secretion and hyperactivity of the thyroid hormones. It occurs in two major forms: (i) Diffuse toxic goiter (Graves’ disease, Exophthalmia goiter) characterized by thyrotoxicosis and ophthalmopathy; and (ii) Toxic nodular goiter (Plummer’s disease) which occurs in older patients of non-toxic goiter, and in these ophthalmopathy is not marked.

Thyroid Medicines Classification

The following classification of Antithyroid drugs is based on their mode of action:

• Inhibitors of thyroxin synthesis Propylthiouracil
1. Methylthiouracil
2. Methimazole
3. Carbimazole
• Drugs that destroy thyroid tissue
1. Radioactive iodine (1131)
• Antiadrenergic drugs
1. Propranolol
2. Guanethidine
• Drugs with uncertain mode of action
1. Potassium iodide
2. Sodium iodide
3. Lugol’s iodine (Strong Iodine Solution
4. Thioamides

Propylthiouracil, a thioamide, is the prototype in the group, and has completely replaced the parent compound thiouracil. It inhibits the synthesis of the thyroid hormones in usual doses, but does not inactivate or interfere with the action the already formed and stored thyroxin in the gland.

Antiadrenergic Drugs: Propranolol, the beta-blocker, and Guanethidine, the adrenergic neuron blocking agent, may be used as adjuncts to Antithyroid therapy to control the adrenergic mediated symptoms of thyrotoxicosis, like tachycardia, palpitation and hypertension. They have no effect on the underlying cause of the disease.

Iodide: Iodide is the oldest agent used in the management of thyroid disorders. It is used in the treatment of iodine-deficiency goiter, and this prevents endemic goiter and cretinism.

Drug Therapy of Thyrotoxic Crisis: Thyrotoxic crisis (thyroid storm) is an exacerbation in the ‘intensity of the features of thyrotoxicosis. It is usually precipitated by surgery, and is most likely to occur in patients who have been inadequately prepared pre-operativity. This crisis has become uncommon with the growing use of beta-adrenoceptor blockers in the pre-operative treatment of Thyrotoxic patient. Plasmaphoresis is an adjunct of therapy of thyroid crisis.